Hydraulic system



0d. l5, 194.5. A. H. ADAMS ETAL HYDRAULIC SYSTEM ATT RNEY Patented Oct. 15, 1946 leans HYDRAULIC SYS TEM Arben H. Adams and Theodore S. Tucker, North Hollywood, Calif., assignors, by mesne assignments, to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application October 19, 1942, Serial No. 462,614

(Cl. SII-54.5)

12 Claims. l

This invention relates to iiuid actuating systems, and more particularly to fluid actuating systems incorporating automatic means for compensating for fluid expansion or contraction, or other factors aecting volume.

An object of the invention is to provide a fluid actuating system wherein the driven member is held in registration Within close limits.

Another object is to provide electrical means for compensating a uid actuating system for changes and fluid volume.

Another object is to provide a fluid actuating system having indicating means to show lack of registration of driving and driven parts.

Another object of the invention is to provide electrical contact means for compensating 'a fluid system.

Another object is to provide a iiuid actuating system having automatic indexing means when the driving member reaches the extremes of its movement.

Another object is to provide automatic electrical means for indexing a fluid system at the extremes of movement of the driving member.

Other objects and advantages of the invention will be apparent in the following description and claims.

t. In the drawing forming a part of this specificaion:

Figure 1 is a schematic showing of a fluid actuating system having electrical compensating means and a fluid indexing means; and

Figure 2' is a schematic showing of a fluid actuating system having electrical compensating means as well as electrical indexing means.

In this specification the word synchronization will be used to denote a correspondence of position of driving and driven units while moving. In other words, this relates to a dynamic condition. The word registration will be used to denote a correspondence of position between driving and driven units while both are stationary. This word therefore refers to a static condition. The word indexing will be used to describe the act of registering driving and driven units at a selected positionv of one unit, as at the ends of the stroke of the driving unit.

Referring to Figure 1, a master cylinder unit I is connected by a conduit I2 to e, motor unit I4. The master unit includes a cylinder housing It, a piston I 3 movable therein connected to a piston rod 2G. Piston rod 26 is actuated by a manual lever 22 pivoted at 2liI and connected by a link 26 to piston rod 2f). The lever 22 is maintained in place by a brake shoe 23 contacting a braking surface 3E. Brake shoe 28 is Vlifted when movement of the lever is desired and this is performed by manually depressing thumb lever 32 which lifts rod 32, shown largely in dotted outline.

Motor cylinder Illincludes a housing 36, a piston 38 connected to a piston rod 40, and a tension spring 42 connected to the housing 36 and rod 4H, to urge piston 38 toward the left end of cylinder 36.

In normal operation, clockwise movement of lever 22 creates pressure on the fluid in the master cylinder I0 forcing it through conduit I2 into motor cylinder I4. The fluid causes piston 38 to move the exact amount that piston I8 moves, inasmuch as cylinders I6 and 36 are the same size.

This fluid actuating system is subject .to thermal expansion and contraction, however, which increases or decreases the volume of the uid in conduit I2 or in cylinders I6 and 36 causing a lack of registry between the master and slave pistons I8 and 38 respectively. For example, the actuating system may be used on an airplane, whereby the pilot controls the throttle of an'engine placed in the wing of an airplane.. When the airplane is flying in the higher cold altitudes the uid in conduit I2 contracts causing the piston 38 to move to the left, upsetting the throttle setting. Or7 when the plane lands, the wing may be exposed to the suns rays, heating up the fluid until the piston 38 moves to the right, giving a change in throttle setting.

The invention includes means to compensate for this iiuid expansion and contraction so that the motor cylinder 3B remains at the point to which it was moved, within extremely close limits. Formed on motor piston rod 40 is a projection All. A slide member 46 sliding on a base 48 is adapted to be contacted by projection 44. The clearance between projection Il and slide 46 is made extremely small and may be .003 of an inch on an end. vElectrical current is supplied to projection M and a circuit is completed when it contacts slide d5, sending current to a reversible electric motor 5l?. Motor 50 drives a reversible pump 52 which is connected by a branch conduit 5d to conduit I2. Pump 52 adds or subtracts fluid from conduit 54, removing or adding it to a reservoir 56, all depending upon whether there is expansion or contraction.

The electrical circuit is supplied by a, battery (near control lever 22) connected by a wire 60 to a switch SI. Switch SI is normally closed but is opened by depressing thumb lever 32. Leading from switch SI isa Wire 62 which leads to projection 44. Switches S2 and S3 connect the wire 62 to wires 64 or 68 respectively leading to reversible motor 56, causing it to rotate in one direction or another according to which wire delivers the current. In actual practice micro switchesare used for switches S2 and S3. In that event, wire 62 is merely forked and connected to wires 64 and 66 through microA switches which are normally open. Projection M then lmerely serves as a mechanical block for closing the switches. Micro switches normally close on a movement of .002' of an inch. Thus if a clearance of .003 of an inch is allowed at each end, .002 of which is taken up by micro switch movement, there will be a. neutral free area of .G01 of an inch.

Since it might possibly happen that the motor and master cylinders will get out of registration in spite of the compensating device, an indicator is provided for this purpose. The indicator includes a battery G8 having parallel connections through resistors 'I0 and I2 from positive to negative. Take oiTs 14 and 'I6 are provided for each resistance and are mechanically moved along their respective resistance by master piston rod 2B and motor piston rod 40 respectively. The take-offs I4 and 'I6 are connected to a polar galvanometer 18. Since the voltages at corresponding points on the resistances 'I9 and 'I2 are equal, any lack of registration will be shown up quantitatively and qualitatively on the galvanometer 18.

Having been informed by galvanometer 18 of a lack of synchronism, the operator may compensate for the same in two ways. He may move the lever 22 in the direction to cause pump 52 to correct the system and at the same time keep a switch Slil, in shunt to switch SI, closed. This may be continued until the galvanometer reads zero. Ory he may use the hydraulic indexing or registering means which will now be explained. Mounted on master cylinder I8 is a valve housing 80 having conduit 82connected from it to conduit I2. Also connected to the housing is a pressure conduit 84 and an exhaust conduit 86. A valve slide member 88 is connected `to lever 22 by rods 90 and SZand rocker arm 94. When valve slide 88 is at the right end of housing 88 conduit I2 is connected to exhaust and when valve slide 88 is to the left, conduit I2 is connected to pressure.

The operation of the system of Figure 1 is as follows: The operator grasps lever 22, depressing thumb lever 32, lifting brake shoe 38 and opening switch Sl. To move motor piston 38 to the right, the lever is moved clockwise and the pressure created by piston I8 is transmitted through conduit I2 to piston 38, causing it to move a corresponding amount. When the motor piston moves to the desired amount the thumb lever 3?. is released, lever 22 is locked in position and switch SI closed. The movement of motor piston rod 48 also moves slide 46 with it, closing switch S3. When switch S3 is closed current ows through wire 65 to motor 58, causing pump 52 to subtract or withdraw uid from conduit I2. This action continues until motor piston 38 moves .002 of an inch to the left, opening switch S3 and breaking the circuit to motor 50. Thus, the motor piston moves a slight amount after being set by the master unit, but this movement is so slight that it does not interfere with practical operations.

If the fluid in conduit I2 should expand due to heat or otherwise, the switch S3 will close after piston 38 has moved .002 or .003 of an inch. This starts motor 50 to act on pump 52 to subtract fluid from conduit I2 until motor piston 38 returns to its original position and again opens switch S3. If the uid should thermally contract in conduit I2 or elsewhere, or become less because of leakage, the spring 42 will force piston 38 to the left. When this movement exceeds .003 of an inch, projection 44 will close Switch S2 and operate motor 5D inthe opposite direction to add fluid to conduit I2 from reservoir 56 until the motor piston 38 returns to its original position.

If the operator should now desire to move motor piston 38 to the left, he moves lever 22 in a counter-clockwise direction. Master piston I8 thereupon moves to the left, relieving fluid pressure momentarilyy allowing motor spring 42 to move motor piston 38 to the left a corresponding amount. At the end of the movement, switch S2 will still be closed and the motor will operate until motor piston 38 moves about .002 of an inch to the right. Thereafter leakage and thermal expansion and contraction will be compensated for in the manner described above.

Since a continued series of operations of the master cylinder in the same direction might result in a lack of synchronisrn between master and motor units, galvanometer 'i8 is provided to indicate this. Registration is important when it is desired to move the motor cylinder to a given position by moving lever 22 to a predetermined position. The bridge system connected to galvanometer 'I8 indicates the direction and the amount of lack of synchronism.

Lack of registration may be corrected by moving lever 22 to close the proper switch S2 or S3 at the same time keeping switch SIDI! closed. Thus if there is too little fluid in the system, piston I8 should be moved to the left, closing switch S2, which in turn actuates motor 5D, causing pump 52 to add to the system. By moving piston I8 slowly to the left, this adding action may be continued until the desired amount of iluid is added, as indicated by meter 18. If there is too much liquid in the system, piston I8 may be moved to the right until switch S3 is closed. This causes pump 56 to subtract liquid to the system, and by moving piston I8 to the right at the same rate of speed, this action may be continued until the desired amount is subtracted.

Or, alternatively, the lever 22 may he moved to one extreme or the other with switch SIUG in open position. If moved to the left, valve 8B will move to the right connecting conduit I2 to exhaust, relieving any excess fluid since spring 42 moves motor piston 38 to the extreme left. If

i lever 22 is moved to the extreme right and the brake is set, pressure uid flows through valve 88 to conduit I2 to supply any deciency until motor piston 38 moves to the extreme right of its cylinder. If extremely high pressures are used they will merely force master piston I8 to the left also, closing valve 88 through lever 22.

From the foregoing description of Figure l, it will be apparent that there are three cooperating parts of the invention, all necessary for the single result of a registered and compensated fluid actuating system. Thus, the compensating system counteracts expansion, contraction and leakage. The indicating system shows whether or not there is registration between the driving and driven parts. The compensation system, or the separate hydraulic indexer, valve 88, may be used to restore registration as previously explained.

The device of Figure 2 will now be described. It is essentially the same as Figure 1 except that the hydraulic indexer (valve 88) is replaced by an electrical indexer or means to register the driving and motor units at the extremes of the strokes. A lever |22 is connected by a link l26 to a piston rod |28 connected to a piston H8. Piston IIS reciprocates in a cylinder IIB and forms a master cylinder unit H0 with the same.

"5 A conduit ||2 connects cylinder ||6 .to a motor cylinder |35` having a piston |38 reciprocable therein and urged to the left by a compression spring |42. Connected to piston |38 iS a DSOII rod |40 having a projection |134 engaging a slide member |45 slideable on a base |58. The motor unit is H4. y

Branching from conduit 2 is a conduit |54 controlled by a solenoid operated poppet |52 controlling the flow of fluid under pressure. A second branch |82 is controlled by a solenoid operated poppet |55 controlling the ow of iiuid to exhaust.

The compensatingY circuit includes a battery |58 connected by a wire |66 to a switch S| l which in turn is connected by a wire |52 to projection |54. Switches S|2 and S53 are placed on either side of projection |44 and are connected to wires |64 and |65` respectively, wire |65 leading to pressure solenoid |80 and wire |66 leading to exhaust solenoid |28. The operation is much the same as in Figure l, fluid being added or subtracted from conduit H2 .by valves |52 and |55 respectively.

The electrical indexer of Figure 2 will now be described. Branching from battery |58 is a wire 250 passing near the motor unit H4 where it is connected to a. normally open switch SI4. Leading from switch SIG is a wire 252 leading to a normally closed switch Si 5. Switch Sie is in turn connected to exhaust solenoid wire |55. Thus, if master piston rod |29 is moved toward the extreme right, and there is more fluid in conduit |42 than normally prevails, motor piston |38 will be ahead of master piston H8. For this reason, motor piston |38 will reach the end of its stroke and switch SM will be closed by an actuator ll movable with the rod |55 before switch SI5 is opened by an actuator |202 on rod |20, exhausting the excess uid by valve 156 until the master piston also reaches the end of its stroke, at which time switch Si 5 is opened, breaking the circuit, and closing the connection to exhaust.

Branching from the left end of wire 205 is a wire 264 leading to a normally open switch Sie. Switch S|6 is connected to a wire 255 leading to a point near the motor cylinder to a normally closed switch SI1, the other end of which is connected t exhaust wire |54. Thus, if there is too much fluid in the connections for registration and lever |22 is moved to the extreme left, switch S| will be closed by an actuator IZili on rod mi! before switch Sil is opened by an actuator |5ll2. This opens exhaust valve |55 allowing the fluid to escape to exhaust until motor piston |38 also reaches the end of its stroke. At this point switch nected to a wire 2|4 leading toward themotor unit to a, normally closed switch S2 which in turn is connected to pressure solenoid wire |56. When there is too little iiuid for registration and lever |22 is moved toward the extreme right, it will close switch S29 while switch S2I is closed, passing pressure fluid into the system. When registration is achieved, motor piston |38 will open switch S2 stopping the flow of uid.

The indicator device of Figure 2 is the same as that of Figure l, and includes a battery |68, parallel resistances |70 and |72, and wipers |14 and |15, as well as a galvanometer l '53.

The operation of the system of Figure 2 is as follows: Movement of lever |22 moves piston H8, which in turn, through fluid compression or the tension of spring |42, moves motor piston |38 a corresponding amount and direction. Motor piston rod Idil moves slide |525 with it, then projection |54. After the initial correction as described with reference to Figure l, switches SI2 and S|3 open the pressure and exhaust valves |52 and |56 respectively, depending upon whether there is contraction or expansion.

Lack of registration is indicated by galvanometer |58, in which case lever |22 may be moved to one extreme or the other to index or synchronize the master and slave units. If there is too much fluid in the connections, movement of lever |22 to the right 'will close switch Sill, opening exhaust valve |56 until lever |22 reaches the extreme right position, at Which time switch S|5 is opened. Likewise, movement of lever |22 to the left closes switch SIB, opening exhaust valve |55 until motor piston |38 reaches the extreme left, opening switch SH.

Too little fluid for registration results in switch S25 closing on clockwise movement of lever |22, opening pressure valve 52 until motor piston |38 opens switch S2|. Leftward movement of lever |22 closes switch SIB adding fluid until lever |22 can go to the extreme left and open switch S 9.

The word uid has been used in describing the invention, since gas or liquid can be used S|l lwill be opened, -breaking the circuit and allowing valve |56 to close.

Branching from wire 25) near the right end is a wire 268 leading to a normally open switch SIB. This switch is connected to a wire 229 leading toward the master cylinder to a normally closed switch Si. Switch SiS is connected to pressure solenoid wire ISE. Thus, when there is too little fluid in the connections, and lever |22 is moved toward the extreme left, motor switch S98 will close before master switch SIB opens. rhis opens pressure valve |52 until sufficient :duid has entered the system so that lever |22 can be moved to the extreme left, at which point it opens switch S|9 breaking the circuit.

Branching from wire 255 near the left is a wire 2 I2 connected to a normally open switch S20 conas the operating medium. It will 'be appreciated, however, that for best results an incompressible liquid is preferable.

Although this invention has been described with reference to particular embodiments thereof, it is not limited to these embodiments nor other- Wise except by the terms of the following claims:

We claim:

1. A uid actuating system comprising driving means, driven means, a fluid connection between said means whereby said driven means moves in response to said driving means, movable means moved by said driven means, switch means actuated by contact of said driven means with said movable means, a connection to exhaust, a valve to control the same, a connection to pressure and a valve to control the same, said valves being controlled vby said switch means whereby fluid is removed or added to said driving, driven and connection means depending upon the direction of contact of said driven means with said movable means.

2. A uid actuating system comprising driving means, driven means, a fluid connection between said means whereby said driven means moves in response to said driving means, movable means moved by said driven means, switch means actuated by contact of said driven means with said movable means, a connection to exhaust, a valve to control the saine, a connection to pressure, a valve to control the same,said valves being controlled by said switches Awhereby fluid is removed or added to saidv driving, driven and connection means depending upon the direction of contact of said driven means with said movable means, and means to render said'switches inoperative when said driving means is operating to move said driven means.

3. A fluid actuating VSystem comprising driving means,'driven means, a fluid connection between the same; means to compensate for volume changes in thefluid, means to indicate the state of registration of said drivingand driven means, and indexing means comprising a valve adapted to connect said system to exhaust at one extreme of movement o f said driving means and to` connect said system to pressure at the other extreme of movement. i

4. In a fluidactuating system including driving means, driven means, a fluid connection between the same; an indexing valve connected to said system and actuated by saiddriving means to connect said system to pressure at one extreme of movement of said driving means and connect said system to exhaust at the other extreme of movement of said driving means.

5. In a iiuid actuating system including driving means, driven means, and a fluid connection between the same; an electrical indexer comprising interconnected switch means at both ends of the strokes of both'of said driving and said driven means, and fluid adding andsubtracting means to index said driving and vdriven means, and operated by said switch means.

6. A fluid actuating system comprising driving means, driven means, a fluid connection between said means, electrical means compensating for fluid volume changes within close limits, means to index said driving and said driven means, and means to inoicate the state of registration of said driving and said driven means, said indicator means comprising a source of electrical potential, two resistances connected to said source, a wiper on each said resistance, one moved by the driving means and one moved by said driven means, and a polar galvanometer connected to said wipers.

7. A fluid actuating system comprising driving means, driven means, a fluid connection between the same whereby said driven means moves in response to said driving means volume compensating means to add and subtract iiuid to and from said driving, driven, and connecting means, a member moved by said driven means, switch means actuated by contact of said member with the driven means to actuate said volume compensating means to add or subtract fluid depending upon the direction of contact, and means interlocked with said driving means to render said rst-mentioned switch means inoperative when said driving means is operating to move said driven means.

'81y A fluid actuating system comprising driving means, driven means, a uid connection between said means whereby said driven means moves in response to said driving means, moveable means moved by said driven means, switch means actuated by contact of said driven means with said movable means, compensating means to add and subtract fluid from driving, driven and connecting means and controlled by said switch means, and electrical indexing means connected to said compensating means and operative at at least one point of stroke of the driving means to actuate 8 saidcompensating means to register said driving and 'said driven means.

9. A fluid actuating system comprising driving means, driven means, a iiuid connection between the same, moveable means moved by said driven means, rst switch means actuated by contact of said driven means with said moveable means, a fluid connection 'to exhaust, a valve to control the same, a fluid connection to uid under pressure, a valve to control the same, a connection to said valves` from the first switch means to selectively actuate said valves depending upon the direction of contact of said driven means with said moveable means to add or subtract fluid for compensating purposes, and a second switch means operable at at least one point in the stroke of the driving means, and connected to said valves for control of the same, to register said driven means with said driving means.

10. In a fluid actuating system including driving means and driven means movable through corresponding ranges and a fluid connection between said means whereby said driven means is moved in response to movement of said driving means; indexing means responsive to movement of said 'driving means into one end of its range of movement for varying the volume of the fluid in Ithe system in direction to move the driven means into its corresponding end position, and means responsive to movement of said driven means into its corresponding end position for disabling said indexing means.

11. A fluid actuating system comprising driving means, driven means, a fluid connection between said means whereby said driven means moves in response to said driving means, a first member moved by said driven means, a second, freely movable member in the path of said rst member and adapted to be contacted by and moved only by contact with said rstmember and be frictionally retained in whatever position it is moved to by said driving means, means to vary the volume of fluid in said system to compensate for fluid volume changes, switch means actuated by contact of said first member with said second member to actuate said volume varying means in such direction as to reverse the movement of said driven means, and means for disabling said volume-varying means during movement of said driving means.

12. A fluid actuating system comprising driving means, driven means, a fluid connection between said means whereby said driven means moves in response to said driving means, a rst member coupled to said driven means for movement therewith and a second, freely movable member in the path of said rst member and adapted to be contacted by and moved only by contact with said rst member and be frictionally retained in whatever position it is moved by said driving means, said rst member having a small range of movement with respect to said second member, compensating means for varying the volume of fluid in said system to compensate for fluid volume changes, switch means selectively responsive to relative movement of said first member in either direction with respect to said second member for actuating said compensating means to vary the volume of fluid in such direction as to reverse the direction of movement of said driven means and said rst member, means for disabling said compensating means during movement of said driving means.

ARBEN H. ADAMS. THEODORE S. TUCKER. 

